AD652
The one-shot capacitor controls the pulse width of the
frequency output. The pulse is initiated by the rising edge of the
clock signal. The delay time between the rising edge of the clock
and the falling edge of the frequency output is typically 200 ns.
The width of the pulse is 5 ns/pF, and the minimum width is
about 200 ns with Pin 9 floating. If the one-shot period is
accidentally chosen longer than the clock period, the width of
the pulse defaults to equal the clock period. The one-shot can be
disabled by connecting Pin 9 to +VS (Figure 17); the output
pulse width is then equal to the clock period. The one-shot is
activated (Figure 18) by connecting a capacitor from Pin 9 to
+VS, −VS, or Digital Ground (+VS is preferred).
DIGITAL GROUND
Digital Ground can be at any potential between −VS and
(+VS – 4 V). This can be very useful in systems with derived
grounds rather than stiff supplies. For example, in a small
isolated power circuit, often only a single supply is generated
and the ground is set by a divider tap. Such a ground cannot
handle the large currents associated with digital signals. With
the AD652 SVFC, it is possible to connect the Digital Ground to
–VS for a solid logic reference, as shown in Figure 19.
+V
S
AD652
+V
S
SYNCHRONOUS
VOLTAGE-TO-
FREQUENCY
CONVERTER
5V
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
REFERENCE
AD652
SYNCHRONOUS
VOLTAGE-TO-
FREQUENCY
CONVERTER
5V
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
REFERENCE
C
INT
ONE
SHOT
R
L
5V
–
IN
+
FREQ
OUT
V
20kΩ
1mA
Q
CK
"D"
CLOCK
ONE
SHOT
D
AND
20kΩ
Q FLOP
C
OS
1mA
Q
CK
"D"
D
AND
Q FLOP
–V
S
Figure 19. Digital GND at −VS
Figure 17. One-Shot Disabled
AD652
SYNCHRONOUS
VOLTAGE-TO-
FREQUENCY
CONVERTER
5V
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
REFERENCE
ONE
SHOT
20kΩ
1mA
Q
CK
"D"
D
AND
C
OS
Q FLOP
ANY AC GND
(+V , –V , OR DIGITAL GND)
S
S
Figure 18. One-Shot Enabled
Rev. C | Page ±3 of 28
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